Three novel anabaenopeptins from the cyanobacterium Anabaena sp.

Three new cyclic peptides, anabaenopeptins NZ825, NZ841, and NZ857, were isolated from the hydrophilic extract of the cultured cyanobacterium Anabaena sp. The planar structure of the compounds was determined by homonuclear and inverse-heteronuclear 2D-NMR techniques as well as high-resolution mass spectrometry. The absolute configuration of the asymmetric centers was studied using Marfey's method for HPLC. This is the first report of anabaenopeptins that contain N-methyl glycine instead of the common N-methyl alanine. The incorporation of N-methyl glycine into the cyclic portion of the compounds results in their appearance as a mixture of two, equally stable, conformers, instead of the one distinct conformer in anabaenopeptins that contain N-methyl alanine or N-methyl homotyrosine. The three compounds were tested for inhibition of serine proteases and found to be not active.